To enable forming of a metallic exterior material high in design effect having a pattern depth of 3 to 8 mm maximum by providing preliminary rolls at the entrance of emboss rolls and applying tension between both the rolls.

Tension is applied between the emboss rolls having a pattern depth of 8 mm and the preliminary rolls provided at the entrance of the emboss rolls to enable adjustment of the material pulling-in quantity with the emboss rolls to effect stable forming. Fine rugged patterns are formed on the preliminary rolls and an offset is provided to the vertical joint positions of the emboss roll patterns, enabling patterning of vertical walls formally impossible heretofore to mold a metallic exterior material having a high-grade feel.